Elevated presence of cell-free DNA (CFD) in blood has been linked to cancers, sepsis, radiation poisoning, brain damage, and stroke. The use of CFD as a biomarker for diagnosing such conditions has been inhibited by the complexity and expense of current methods for determining the concentration. Methods for determining CFD concentration in biological samples such as serum include labeling with DNA responsive fluorescent dyes such as PicoGreen® from Life Technologies. Although capable of measuring DNA directly in serum, such methods suffer from high background noise signal and reduced sensitivity due to the presence of serum which exhibits substantial and variable autofluorescence. Moreover, spectroscopic determination of DNA concentration may typically be performed using UV absorbance, however, serum components also absorb at the relevant wavelengths, which complicates the analysis. Alternative high sensitivity methods for measuring CFD typically involve labor- and time-intensive steps including DNA extraction and purification followed by gel electrophoresis and/or quantitative real-time polymerase chain reaction (qPCR).
Microfluidic systems, including “lab on a chip” or “lab on a disk” systems continue to be in development. See, Lee, B. S., et. al., “A fully automated immunoassay from whole blood on a disc,” Lab Chip 9, 1548-1555 (2009) and Madou, M. et. al., “Lab on a CD,” Annu. Rev. Biomed. Engr. 8, 601-628 (2006), which articles are hereby incorporated by reference in their entirety for any purpose.